The present invention relates to a plastic pipe cutting device adapted for cutting plastic pipes and, more particularly to such a plastic pipe cutting device, which automatically pulls the cutter back to the stand-by position after each cutting operation.
A conventional plastic pipe cutting device, as shown in FIG. 1, is generally comprised of a housing 1, a cutter holder 5 slidably mounted in the housing 1, the cutter holder 5 having a bottom rack 7 and a side rod 8, a cutter 6 fixedly mounted on the front side of the cutter holder 5, a tensile spring 10 connected between the side rod 8 of the cutter holder 5 and a rear part of the housing 1, a handgrip 2 fixedly connected to the housing 1 at a bottom side, a lever 3 pivoted to the housing 1 in front of the handgrip 2, a compression spring 4 connected between the lever 3 and the handgrip 2, and a ratchet mechanism a pivoted to the lever 3 below the rack 7 of the cutter holder 5. The ratchet mechanism a comprises a ratchet wheel 11 meshed with the rack 7 of the cutter holder 5 and rotated to move the cutter holder 5 forwards or backwards, a stop block 13 mounted on the lever 3, a push block 12 pivoted to the lever 3 and supported on a spring 14 in the lever 3, a pawl 15 pivoted to the housing 1 and adapted to limit the direction of rotation of the ratchet wheel 11, and a control rod 16 adapted to release the pawl 15 from the ratchet wheel 11. When alternatively pressing and releasing the lever 3, the push block 12 is forced to rotate the ratchet wheel 11, thereby causing the ratchet wheel 11 to move the cutter holder 5 forwards, and therefore the cutter 6 cuts the loaded plastic pipe 9. During cutting, the pawl 15 stops the ratchet wheel 11 from reverse rotation. After cutting, the control rod 16 is pushed forwards to disengage the pawl 15 from the ratchet wheel 11, enabling the cutter holder 5 to be pulled back by the tensile spring 10. This structure of plastic pipe cutting device is still not satisfactory in function. The drawbacks of this structure of plastic pipe cutting device are outlined hereinafter.
1. Because driving force is transmitted from the lever 3 to the rack 7 of the cutter holder 5 through the push block 12 and the ratchet wheel 11, much effort is required to move the cutter holder 5.
2. The ratchet wheel 11 wears quickly with use. When started to wear, the ratchet wheel 11 may slip on the rack 7 of the cutter holder 5.
3. The pawl 15 wears quickly with use, and tends to slip on the ratchet wheel 11. Further, the control rod 16 may be driven accidentally to disengage the pawl 15 from the ratchet wheel 11.
4. The cutter holder 5 can be pulled back only after the control rod 16 had been pressed to disengage the pawl 15 from the ratchet wheel 11. If the user forgets to disengage the pawl 15 from the ratchet wheel 11 for enabling the cutter holder 5 to be pulled back by the tensile spring 10, the cutter 6 is not received inside the housing 1 and may injure the people by an accident.
The invention has been accomplished to provide a plastic pipe cutting device, which eliminates the aforesaid drawbacks. It is one object of the present invention to provide a plastic pipe cutting device, which can be operated with less effort to cut the loaded plastic pipe efficiently. It is another object of the present invention to provide a plastic pipe cutting device, which automatically pulls the cutter back to the stand-by position after each cutting operation. It is still another object of the present invention to provide a plastic pipe cutting device, which drives the cutter positively without a miss. It is still another object of the present invention to provide a plastic pipe cutting device, which is safe in use. According to one aspect of the present invention, the plastic pipe cutting device comprises a housing, a cutter connected to a tensile spring at a rear side in the housing and adapted for cutting a plastic pipe inserted into the housing, a lever pivoted to the housing and adapted to drive the cutter, a driving block supported on a spring in the lever and adapted for turning with the lever to move the cutter forwards, a stop member adapted to stop the cutter from backward movement, and a push block slidably mounted in the housing and adapted to push the stop member away from the cutter for enabling the cutter to be automatically pulled back by the tensile spring to its stand-by position after the loaded plastic pipe had been cut. According to another aspect of the present invention, the driving block is driven to move the cutter directly when alternatively pressing down and then releasing the lever. According to still another aspect of the present invention, the rack of the cutter is formed of a series of teeth sloping in one direction, therefore the driving block does not slip on the rack when turned with the lever to move the cutter. According to still another aspect of the present invention, the stop member stops the cutter from backward movement during forward cutting operation, preventing the occurrence of an accident.